Answer
Changes in geographic range could allow species/populations to switch from isolation to overlap. The latter case would allow interbreeding, with the resulting gene flow keeping two populations in the same species, an example of evolutionary stasis. Also, shifting geographic range would force species to adapt to several sets of conditions across their shifting range, again leading to little or no evolutionary change/stasis.
Work Step by Step
First look at the definition of evolutionary stasis: a period of little or no evolutionary change. Then consider how shifting geographic range could prevent evolution. Two possibilities (there could be others) would be gene flow to prevent a species/population from adapting to one specific place and adaptation to multiple geographic places preventing speciation.
